Traditional wear systems use external lubricants, such as oil or grease, to increase the wear resistance and reduce frictional losses between moving contacting components. However, such external lubricants often must be replaced periodically and may be unevenly distributed over the wear surface, resulting in increased cost and inefficiency of the wear system. In addition, traditional external lubricants are not desirable, for example, in the areas of food processing or photocopying where product contamination is a concern.
The need for external lubricants may be reduced or eliminated by the use of polymeric contacting components. Polymeric components may be easily and inexpensively manufactured by such processes as injection molding to form intricately shaped components such as gears, cams, bearings, slides, ratchets, pumps, electrical contacts and prostheses.
Polymeric contacting components provide an economical and essentially maintenance free alternative to typical prior art non-polymeric contacting components. Components formed from polymeric compounds have greater shock and vibration dampening, reduced weight, enhanced corrosion protection, decreased running noise, decreased maintenance and power use, and allow increased freedom of component design over non-polymeric components. Internal lubricants, such as polytetraflurorethylene, graphite, molybdenum disulfide, and various oils and reinforcing fibers may be included in polymeric components to enhance wear resistance and decrease frictional losses. However, typical prior art internal lubricants may be costly and increase the complexity and number of processing steps.
The prior art discloses various modified polymers having improved sliding properties and increased wear resistance. For example, U.S. Pat. No. 4,174,358 discloses toughened thermoplastic compositions having a polyamide matrix resin and at least one branched or straight chain toughening polymer. The polymer may be elastomeric or thermoplastic. Examples of suitable toughening polymers include synthetic and natural rubbers such as butadiene/acrylonitrile rubber, styrene/butadiene rubber, buna rubber, isobutylene, isoprene, natural rubber, ethyl acrylate, butyl acrylate rubbers, etc.
U.S. Pat. No. 4,371,445 discloses tribological systems of plastic/plastic pairings in which at least one of the partners is a plastic containing polar, cyclic compounds. The cyclic part of the molecule on at least one side may be coupled directly to an atom of Group V or Group VI of the Periodic Table or the ring may contain atoms of Group V or VI. An optional auxiliary sliding partner may be formed from a polyalkylene. A partner may consist of several materials, such as a mixture of two or more of polyethylene, polypropylene, polyisobutylene, polystyrene, polytetrafluoroethylene and polyvinylidene chloride.
U.S. Pat. No. 5,039,714 discloses a rubber-modified polystyrene composition containing a polystyrene, dispersed particles of elastomeric polymers and optionally polydimethylsiloxane and at least one member selected from mineral oil, and metallic salts or amides of higher fatty acids. The elastomeric polymers may include polybutadiene and styrene-polybutadiene copolymers. Rubber-modified polystyrene may be obtained by mixing and polymerizing styrene monomer in the presence of styrene-butadiene block copolymers or polybutadiene.
U.S. Pat. No. 4,987,170 discloses a styrene resin composition including styrene polymer, dimethylsilicone oil and a maleic anhydride monomer or a maleic anhydride-styrene copolymer. The styrene polymer may be modified with a rubber-like polymer, such as polybutadiene, styrene-butadiene copolymer, butadiene-acrylonitrile copolymer, ethylenepropylene-diene terpolymers and butadiene-acrylate copolymers. For example, a maleic anhydride-styrene copolymer may be modified with a rubber-like polymer.